Raw cotton (gin output) is dark brown in colour due to the natural pigment in the plant. The cotton and textile industries recognise a need for bleaching cotton prior to its use in textiles and other areas. The object of bleaching such cotton fibres is to remove natural and adventitious impurities with the concurrent production of substantially whiter material.
There have been two major types of bleach used in the cotton industry. One type is a dilute alkali or alkaline earth metal hypochlorite solution. The second type of bleach is a peroxide solution, e.g., hydrogen peroxide solutions. This bleaching process is typically applied at high temperatures, i.e. 80 to 95° C. Controlling the peroxide decomposition due to trace metals is key to successfully using hydrogen peroxide. Often Mg-silicates or sequestering agents such as EDTA or analogous phosphonates are applied to reduce decomposition. A problem with the above types of treatment is that the cotton fibre is susceptible tendering.
Wood pulp produced for paper manufacture either contains most of the originally present lignin and is then called mechanical pulp or it has been chiefly delignified, as in chemical pulp. Mechanical pulp is used for e.g. newsprint and is often more yellow than paper produced from chemical pulp (such as for copy paper or book-print paper). Further, paper produced from mechanical pulp is prone to yellowing due to light- or temperature-induced oxidation. Whilst for mechanical pulp production mild bleaching processes are applied, to produce chemical pulp having a high whiteness, various bleaching and delignification processes are applied. Widely applied bleaches include elemental chlorine, hydrogen peroxide, chlorine dioxide and ozone.
Whilst for both textile bleaching and wood pulp bleaching, chlorine-based bleaches are most effective, there is a need to apply oxygen-based bleaches for environmental reasons. Hydrogen peroxide is a good bleaching agent, however, it needs to be applied at high temperatures and long reaction times. For industry it is desirable to be able to apply hydrogen peroxide at lower temperatures and shorter reaction times than in current processes. Towards this end, the use of highly active bleaching catalysts would be desirable.
As a particular class of active catalysts, the azacyclic molecules have been known for several decades, and their complexation chemistry with a large variety of metal ions has been studied thoroughly. The azacyclic molecules often lead to transition-metal complexes with enhanced thermodynamic and kinetic stability with respect to metal ion dissociation, compared to their open-chain analogues.
United States Application 2001/0025695, discloses the use of a manganese transition metal catalyst of 1,4,7-Trimethyl-1,4,7-triazacyclononane (Me3-TACN); the transition metal catalyst has as a non-coordinating counter ion PF6−. United States Application 2001/0025695A1 also discloses a manganese transition metal catalyst of 1,2-bis-(4,7-dimethyl-1,4,7-triazacyclonon-1-yl)-ethane (Me4-DTNE); the transition metal catalyst has as a non-coordinating counter ion ClO4−. The solubility, in water at 20° C., of the Me4-DTNE complex having non-coordinating counter ion ClO4− is about 16 gram/Liter. The solubility, in water at 20° C., of the Me4-DTNE complex having non-coordinating counter ion PF6− is about 1 gram/Liter.
US 2002/0066542 discloses the use of a manganese transition metal complex of Me3-TACN in comparative experiments and makes reference to WO 97/44520 with regard to the complex; the non-coordinating counter ion of the manganese transition metal complex of Me3-TACN is PF6−. The X groups as listed in paragraph [021] of US 2002/0066542 are coordinating.
EP 0458397 discloses the use of a manganese transition metal complex of Me3-TACN as bleaching and oxidation catalysts and use for paper/pulp bleaching and textile bleaching processes. Me3-TACN complexes having the non-coordinating counter ion perchlorate, tetraphenyl borate (BPh4−) and PF6− are disclosed. The solubility, in water at 20° C., of the Me3-TACN complex having non-coordinating counter ion ClO4− is between 9.5 to 10 gram/Liter. The solubility, in water at 20° C., of the Me3-TACN complex having non-coordinating counter ion BPh4− is less then 0.01 gram/Liter.
WO 95/27773 discloses the use of manganese transition metal catalysts of 1,4,7-Trimethyl-1,4,7-triazacyclononane (Me3-TACN); the transition metal catalysts have as a non-coordinating counter ion ClO4− and PF6−.
1,4,7-Trimethyl-1,4,7-triazacyclononane (Me3-TACN) has been used in dishwashing for automatic dishwashers, SUN™, and has also been used in a laundry detergent composition, OMO Power™. The ligand (Me3-TACN) is used in the form of its manganese transition-metal complex, the complex having a counter ion that prevents deliquescence of the complex. The counter ion for the commercialised products containing manganese Me3-TACN is PF6−. The Me3-TACN PF6− salt has a water solubility of 10.8 g per liter at 20° C. Additionally, the perchlorate (ClO4−) counter ion is acceptable from this point of view because of its ability to provide a manganese Me3-TACN that does not appreciably absorb water. Reference is made to U.S. Pat. No. 5,256,779 and EP 458397, both of which are in the name of Unilever. One advantage of the PF6− or ClO4− counter ions for the manganese Me3-TACN complex is that the complex may be easily purified by crystallisation and recrystallisation from water. In addition, for example, the non-deliquescent PF6− salt permits processing, e.g., milling of the crystals, and storage of a product containing the manganese Me3-TACN. Further, these anions provide for storage-stable metal complexes. For ease of synthesis of manganese Me3-TACN highly deliquescent water soluble counterions are used, but these counterions are replaced with non-deliquescent, much less water soluble counter ions at the end of the synthesis. During this exchange of counter ion and purification by crystallisation loss of product results. A drawback of using PF6− is its significant higher cost compared to other highly soluble anions.
U.S. Pat. Nos. 5,516,738 and 5,329,024 disclose the use of a manganese transition metal catalyst of 1,4,7-Trimethyl-1,4,7-triazacyclononane (Me3-TACN) for epoxidizing olefins; the transition metal catalyst has as a non-coordinating counter ion ClO4−. U.S. Pat. No. 5,329,024 also discloses the use of the free Me3-TACN ligand together with manganese chloride in epoxidizing olefins.
WO 2002/088063, to Lonza AG, discloses a process for the production of ketones using PF6− salts of manganese Me3-TACN.
WO 2005/033070, to BASF, discloses the addition of an aqueous solution of Mn(II)acetate to an aqueous solution of Me3-TACN followed by addition of a organic substrate followed by addition of hydrogen peroxide.
Use of a water-soluble salt negates purification and provides a solution, which may be used directly, and reduces loss by purification.